A Second Look at Comet C/2023 A3 (Tsuchinshan-ATLAS)!

I had my first look at Comet C/2023 A3 (Tsuchinshan-ATLAS) last night, but my timing sucked, as I didn't locate it until it was close to the horizon and practically lost in the afterglow of the sunset. Tonight I was a bit better prepared, and the comet itself was higher in the sky. It was a beautiful sight, and the finest I've seen since 1997.

My phone is new and I've had little time to learn what it is capable of, but I was pleased with what I got tonight. I was focusing between 1x to as high as 6x magnification. I was also just able to see the comet with the naked eye, but it wasn't obvious.

Comet C/2023 A3 (Tsuchinshan-ATLAS) is getting higher in the western sky each night for the next few weeks, but it will also be growing dimmer as it gets farther from the sun. Get out and see it this week if you can, but if you can't, enjoy these pictures!

Visible now! Comet C/2023 A3 (Tsuchinshan-ATLAS)

 

It's not often that I get to see two rare astronomical phenomena in the same week, but that's what has happened. The other night was an extraordinary display of the aurora borealis in my part of Central California (and most of the rest of the lower 48 states and Alaska). And tonight was my first look at a comet since 2020. Comet C/2023 A3 (Tsuchinshan-ATLAS) is now visible in the west shortly after sunset. It will be rising higher in the sky each night during the remainder of October, but it will be dimmer each night.

I couldn't see it with the naked eye, but the night-shot setting on my smart phone did a decent job of capturing the tail. A short internet search will reveal many spectacular photographs by people with better technology than me. A helpful providing the details of the discovery and location of the comet can be found here.

I've had a spotty relationship with comets over the years. Comet Neowise showed up in 2020, but my photos were not great. The two greatest comets I ever saw appeared in 1996 and 1997, about five years before I got any kind of digital photography equipment. I have great memories of comets Hiyakutake (1996) and Hale-Bopp (1997). They were truly spectacular, and Hale-Bopp was especially bright in the sky when I was crossing the deep dark skies of the Basin and Range province in the middle of the night on a long trip.

If you get a chance over the next few days, take a look west after sunset and see if you can't catch a glimpse of one of the fair treats of the cosmos.

Source: https://www.dailykos.com/stories/2024/10/13/2276491/-Comet-C-2023-A3-Tsuchinshan-ATLAS-is-now-visible-after-sunset?pm_campaign=front_page&pm_source=trending&pm_medium=web

Twice in 2024! Auroras in Central California

Back in May of this year, I saw something I had never seen before: the aurora borealis gracing the night sky over the prairie of the Sierra Nevada foothills. It was an astounding once-in-a-life event. Except it wasn't. The sun has been particularly active this year, and a coronal mass ejection occurred a few days ago that sent charged particles racing towards the Earth. For the second time in my life, I saw the aurora borealis from my home area.

I was teaching an online geology lab and happened across a report that auroras were being sighted in unusual places, and anxiously awaited for my students to finish their work. I checked out my front door and took a shot of the sky in the heavily light-polluted environment, and my phone camera caught the characteristic magenta-pink light. I talked Mrs. Geotripper into taking a late-night drive to the prairie-lands near Willms Road outside of Knight's Ferry on the Stanislaus River.

The lights were immediately evident in my phone camera pictures. They were very dim to the naked eye, but the night shot setting on my phone captured the detailed spires and structures in the lights quite well.

The intensity, color, and pattern of the light changed from moment to moment. It was a nice way to spend an evening!

The lights faded after about an hour and we went home. I hope you got a chance to see them, but if you didn't, please enjoy what we got to see!

The lights were not better or worse than those of last May. They were just different. It was a privilege to be able to view this gift of the cosmos.

 

Part 2: The Limestone Caves of Hawai'i - The Catastrophes at Makauwahi Cave

 

Makauwahi Cave and Sinkhole as it is today

I learned to my great surprise that Hawai'i has a few (very few, really) limestone caves. In part one I talked about the odd origin of Makauwahi Cave on the island of Kauai. In that post we learned that the limestone formed from limestone sand dunes that formed near Poipo Beach. The sand was lithified (glued together), and fresh water dissolved the limestone, forming the cavern, which has around 500 feet of passageways. At the end of the post I alluded to the fact that the cave was witness to three catastrophes that I'll look at today. On reflection, though, I think it's fair to say there were actually four catastrophes, one local, and the others island-wide.

Makauwahi Cave as it might have appeared 1000 B.C. Painting by Dr. Julian Hume

How did these catastrophes transpire? The rock formed around 400,000 years ago, and the passageways grew larger over time. By 7,000 years ago, wave action broke through and for perhaps a few centuries the cave was both a limestone cavern and a sea cave. Marine fossils formed a layer on the cave floor. But the waves may have contributed to the first catastrophe, because a short time later the roof of the cavern collapsed and formed a sinkhole. This is the bowl-shaped pit that is visible in the photo and painting above. The debris plugged the access to the sea, and the cavern and sinkhole filled with fresh water.

But is the collapse of a sinkhole a catastrophe? I guess it depends on your perspective. Some of the rarest of species on an island system with thousands of rare species would be those lifeforms adapted to living in total darkness. There are three blind species living in the darkness of Makauwahi Cave today, an amphipod, an isopod, and a blind spider (below) that feeds on the other two. These creatures have one of the most restricted environments possible on the islands, and the collapse severely restricted their living space. 

Blind cave wolf spider (descended from a surface-dwelling big-eyed spider, so it's sometimes called the no-eyed big-eyed Spider). Photo by Michelle Clark, USFWS.

The real "catastrophe" is what followed the formation of the pond in the bottom of the sinkhole. Animals found their way into the pit, but no way out. The pit became a death trap. Over the next few thousand years huge numbers of fossils, both animals and plants, accumulated in the sinkhole. The organic rich mud (peat) grew to be one of the thickest layers within the pit (see below). Excavations since the 1990s have revealed thousands of specimens that have revealed more about the pre-human environment on Kauai than any other site on the island.

10,000 years of sediment, 33 feet thick, excavated at Makauwahi Cave Source: https://www.hawaii.edu/malamalama/2002/01/LostWorld.html

The primeval world of Kauai and the other Hawaiian Islands was unique. The islands are so isolated that no reptiles, amphibians, or mammals ever reached the islands (aside from seals and bats). The only vertebrate creatures that found their way to the islands were the birds. As a consequence, the environmental niches in the island ecosystem were filled by avian species, and over time they adapted and evolved to fully utilize the resources available to them. Species of hawk and owl filled the role of predator, especially of smaller birds. Ducks and geese grew to immense size and lost the ability to fly, given the lack of larger predators (see below). They took over the niche of plant-eaters and grazers. The honeycreepers were the most astounding example of evolutionary adaptation. From a single Asian finch-like ancestor, more than 50 distinct species evolved, filling the niches occupied elsewhere by parrots, hummingbirds, woodpeckers, and insectivores. Sadly, most of them are extinct and most of the survivors are critically endangered.

Every Hawaiian duck or goose here is now extinct, except for the Nene, on the right. The Nene almost went extinct in modern times. Source: http://www.cavereserve.org/resources/documents/slideshow.pdf

How unique is the Makauwahi fossil record? Of 107 bird species known to have been endemic to the Hawaiian Islands, nearly half (50 species) have been found in and near the sinkhole. Several species were found here and nowhere else on the islands. Some of the unique birds include a flightless goose, a turtle-jawed moa-nalo bird, a long-legged owl that probably fed on other birds, and a little duck with tiny eyes, a flat skull and tiny wings that probably fed on forest insects at night. Several of the birds like the hawk and Laysan duck no longer survive on Kauai, but are still found on other islands. 

Another catastrophe happened about 300-400 years ago. Excavators digging in the sinkhole found their way barred by a layer of boulders weighing as much as 200 pounds. These rocks were a mixture of basalt, lithified dune sands, and coral. The only process that could pile such debris in a sinkhole like this would be a huge tsunami. There much have been a village nearby because the deposit also contains some human artifacts like pieces of canoes, ropes, and ornamental objects. These rocks and other objects were carried over a ridge 27 feet above sea level, meaning the wave must have been much taller.

Humans in Hawai'i have always had to deal with the threat of tsunamis. The location of the islands near the center of the Pacific Ocean means that they can be hit by waves from all directions, generated by earthquakes in places as far-flung as Japan, Alaska, Washington, and Peru-Chile. Strangely, the largest tsunamis of all have been generated by the Hawaiian Islands themselves. Gigantic mega-slides from the flanks of the islands flowing onto the adjacent deep ocean floor have generated waves in excess of a thousand feet high! Thankfully, no such waves have occurred in historic time.

The biggest change at Makauwahi Cave was that the pond had been filled in and it was no longer a fossil trap. But the third and fourth catastrophes become visible in the sediment record of the cave: the arrival of human beings on the islands. 

The landscape surrounding the sinkhole (above) is far, far different than the one that existed prior to a thousand years ago when the first Polynesians reached Kauai, the third catastrophe. Hardly any native vegetation remains. Humans have been successful at geo-engineering their environments to provide the food and resources they need to survive and flourish. The colonizers brought taro plants, coconuts, kukui nuts, and gourds, as well as dogs, pigs, chickens, and whether on purpose or not, the Pacific rat. These invasive plants and animals overwhelmed the native flora and fauna, driving many species to extinction, or to much more limited ranges.

Source: http://www.cavereserve.org/resources/documents/slideshow.pdf

The effect on the birds was truly catastrophic. Evolving in isolation, they had no defense against the mammal invaders. The flightless birds quickly disappeared, and many other species suffered huge declines (above).

Still, from a human point of view, a certain equilibrium had been achieved, even if the native species went into a steep decline. Humans had been expanding across the Pacific islands for centuries, and knew what resources they would need to bring with them when they found new islands to colonize. They also had a social structure that was rather efficient and strict (however unjust to our present sensibilities) that allowed the native Hawaiians to thrive in their new environment, largely operating within the carrying capacity of the lands they were occupying.

The fourth catastrophe began unfolding in 1778 when Captain James Cook and his crew arrived. The full extent of this event is also revealed in the sediments of Makauwahi Cave, but we'll take that up in part 3.

The authoritative source of information on Makauwahi Cave is the book Back to the Future in the Caves of Kaua`i: A Scientist’s Adventures in the Dark; David A. Burney, Yale University Press, 2010.

Visiting Hawai'i...for the Limestone Caverns? (Part one)

People visit Hawai'i for a great many reasons. There are the stereotypical reasons: beautiful beaches, surfing, palm trees, luaus and so on. There are other reasons: a wish to learn about the culture of the many people groups who call the island home, some of them for upwards of a thousand years. There are others who find fascination with volcanoes and lava flows. And the biology! The isolation of the islands has resulted in the evolution of hundreds, even thousands of species that exist nowhere else in the world.

I'm willing to bet that very few people come to the islands to tour the limestone caverns...

Limestone? Caverns? On the Hawaiian Islands?

Outcrop of limestone (!?) on the Mahaulepu Coast of Kauai.

There are actually a great many caves on the islands, but they are not the kind of caves that most people find familiar. They are called lava tubes, and they form when a lava river forms a ceiling of congealed basalt. When the lava flow ends, it drains out the tube leaving behind a long cylindrical cave. Hawaii has one of the longest such caves in the world, Kazimura, with a total length of 40 miles. The much shorter Nahuku Cave (formerly Thurston Cave) in Hawai'i Volcanoes National Park is well-known to park visitors.

Nahuku Lava Tube in Hawaii Volcanoes National Park

But limestone caverns are not a familiar sight on the islands. Before my last trip I didn't know that there were any such caves in Hawai'i. For one, a limestone cavern requires limestone and the islands are composed largely of volcanic basalt. There are coral reefs around the islands in many places and they are composed of calcium carbonate (calcite), the mineral that makes up limestone. But coral forms at sea level, and caverns form from the dissolving action of fresh water, usually above sea level. And the islands are sinking, not rising, so on the face of it there seems to be no opportunity for the development of large bodies of limestone, much less caverns in Hawaii. 

Photo courtesy of Allie Brown

And yet it happened here, on the island of Kauai (and also, upon researching the subject, in downtown Honolulu; check out Moiliili underground caverns if you dare). It was a unique situation, a cavern formed in a sand dune environment. The cavern has been known as Warrior's Cave, Grove Farm Cave, Limestone Quarry Cave and others, but some extensive research revealed the ancient name (from an 1885 student essay) to be Makauwahi, or "source of the smoke".

Sand dunes hardly seem like a place for cavern formation because most of the time sand is composed of quartz and other silicate minerals. Hawai'i's sands are not. They are composed sometimes of basalt fragments (the black sand beaches), but the white or yellow sandy beaches of the islands are mostly composed of bits and pieces of coral reefs, in other words, calcite, the ingredient making up limestone. On the south side of Kauai near the extensive resort complexes of Poipo Beach there are some extensive coral sand beaches. Over the millennia the constant trade winds have blown sand off the beach inland, forming sand dunes above the shoreline. This happened in stages starting about 435,000 years ago during an interglacial period when sea level was higher than today.

Cliff of eolian limestone showing the tilted layers of cross-bedded dune sands at Makauwahi.

When the dunes were stabilized by vegetation, thick layers of soil developed on the surface. Beneath the surface the sand was lithified (glued together) by dissolved calcite and silica derived from the overlying soil. Then the climate changed and dunes moved in again. Over time thick layers of solid limestone resulted from the petrified dunes.

Makauwahi Cave, courtesy of Tylor Ghaffari

The soil layers provide the last part of the process, carbonic acid. Mixed with groundwater, the acid ate away at the lower layers eventually producing the caverns themselves. Later on, dripping and flowing water produced a variety of cavern formations (speleothems) like stalactites, stalagmites, and flowstone. Makauwahi Cave has around 500 feet of passageways, accessed through a small passageway. And so we paid a visit during our field studies exploration of Kauai.

The thing is, if Makauwahi were simply a cave it would merit some attention, but that is not what makes it extraordinary. Makauwahi was the site of three catastrophes, one of which was local, and two others that were island-wide. And from these catastrophes, an amazing story unfolds about life on Kauai, past, present and future. That will be the subject of part two, coming soon (I hope)!

Landslides and Slope Mitigation in California's Great Valley...Wait...What?

 

I used to talk to my students about the geological hazards that we face as inhabitants of California's Great Valley (or Central Valley, for those who don't appreciate its actual greatness). I would go down the list of things to worry about: earthquakes, droughts, wildfires, volcanic eruptions, flooding, and so on. But then I somewhat jokingly described things we didn't have to worry about such as hurricanes (Florida's problem), tsunamis (a problem for coastal cities), tornadoes (Oklahoma's problem), and mass wasting (also known by the generic term 'landsliding').

Unfortunately, over the years I've become aware that some of those unlikely hazards actually can be a factor in living in the valley. We've had a fair number of tornadoes in recent years, including two that came within a few miles of my house (they weren't anything like the monsters of Tornado Alley in the Midwest, but still a bit scary). A powerful tropical storm hit Southern California last summer that came up just short of being a hurricane, and the heavy downpours were statewide. And then there is mass wasting (slope failures and landslides). I know of at least two fatalities caused by mass wasting in the last few years. One was a homeless person who had dug a tunnel into a river embankment that later collapsed, and another was a person who was driving along a freeway in heavy rains when the freeway embankment collapsed as a mudflow and spread across the lanes causing a fatal accident.

The Great Valley is famously flat so mass wasting doesn't seem to be much of a danger to those who live here, since landslides and other slope failures require, well, a slope to happen. But the valley is not quite so flat as people may think. The valley is 400 miles long, and most of it is close to sea level. Much of it is low-lying river floodplains, but other sections sit at slightly higher elevations because of complex history of climate change and glacial ice ages over the last 1,000,000 years. These bluffs and terraces protect my city and others nearby because even the worst floods are contained within the floodplains and do not spill over onto the terrace surfaces where cities like Modesto and Turlock have been built near the Tuolumne River.

During the ice ages glaciers never reached the valley floor, but meltwater from the Sierra Nevada glaciers swelled the rivers to several times their average flow, and they carried tremendous amounts of muddy sediment that spread widely across the valley floor building up alluvial fans. When the glaciers receded, the rivers flowed less, but carried clear water that was more capable of eroding the soft sediments of the alluvial fans, forming channels and floodplains several tens of feet deep. Once these channels developed, floods never covered the terraces again. It's the bluffs that form the boundaries of these terraces that provide the conditions that can result in slope failure.

The heavy rains of 2022-23 led to widespread flooding across many parts of California including some real problems on the Tuolumne River Parkway Trail when I regularly go birdwatching. I wrote about these in January of 2023 in the aftermath of one of the biggest storms. The most serious problem was the access road to our town's water treatment plant. It's on the river floodplain about 60 feet below the river terrace. Slumping had caused major cracks to form in and near the pavement.

Eventually the rains subsided and the soil dried up. The slide seemed to stabilize, but the threat to the roadway remained and would eventually have to be dealt with. That is what was new this week: the cranes and were in place to start the slope mitigation process.

The main problem is that the access road traverses unstable debris and soil that slumped in the 2023 event. They would need to re-engineer the slope by rebuilding it from scratch. Their strategy was complicated by the fact that all the equipment and materials had to traverse the very road they were trying to repair. Truckloads of heavy boulders were going down the road every few minutes. Meanwhile a huge long-reach excavator was digging away at the slope below the road!

After digging away and smoothing off the slope they covered it with felt matting and then started piling many tons of boulders on the slope. The boulders are intended to buttress the slope and hopefully keep it stable during future weather events.

It's a lot of work being done to keep a single paved road open, but it's a pretty important road since it provides the only access to the water-treatment plant for the city of Waterford. And thus we are dealing with slope mitigation in what is supposedly the flattest place in the country!